Radio frequency transmitter, power combiners and terminations therefor

ABSTRACT

A power combiner includes a planar figure-8 shaped primary winding and a planar figure-8 shaped secondary winding; wherein, the planar figure-8 shaped primary winding is substantially overlaid with the planar figure-8 shaped secondary winding. In addition, there is provided a radio frequency (RF) transmitter having a power combiner, where the power combiner includes a planar figure-8 shaped primary winding and a planar figure-8 shaped secondary winding, wherein the planar figure-8 shaped primary winding is substantially overlaid with the planar figure-8 shaped secondary winding.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional application No.61/828,850, filed on May 30, 2013 and incorporated herein by reference.

BACKGROUND

Field of the Invention

The field of this invention relates to radio frequency transmitterspower combiners and harmonic terminations therefor. The invention isapplicable to, but not limited to, power combining techniques.

Background of the Invention

In the field of complementary metal-oxide-semiconductor (CMOS) poweramplifiers, there is a constant demand by consumers for wireless systemsthat are low cost, efficient and reliable. High level integration hasbeen shown in practice to be an effective way to reduce cost and achievecompactness for high volume applications. Currently, almost all poweramplifiers are manufactured with III-V compound semiconductors, as thistype of device has high output power and high power efficiency, whichare desired attributes for many power amplifier applications. It iscurrently very difficult to achieve these specifications using CMOStechnology. However, III-V technologies have high manufacturing costs,as well as being unable to provide a complete system-on-chip (SoC)solution.

Recently, CMOS power amplifiers coupled to power devices have becomemore attractive, partly because the power device technology andprocessing has matured and become lower cost. However, in implementingCMOS power amplifiers and integrating with power devices, there is stilla need to improve the coupling, efficiency, and termination efficiencyof these devices. Such devices are often used in radio frequencytransmitters, for either base station or subscriber unit devices.

Referring first to FIG. 1, a simplified integrated radio frequency poweramplifier (RF PA) system 100 comprises integrated circuit 102 andintegrated power devices 150, 170. Integrated circuit 102 comprisespower inputs 104 operably coupled to isolation transformers 106. Theoutputs of the isolation transformers 106 are operably coupled torespective driver stages 108 wherein the driver stages 108 provideamplified radio frequency signals to inputs of power stages 110, e.g.power amplifiers. In this case, the respective power stages 110 areoperably coupled, via a plurality of bond wires 112, to power combinerdevices 150, 170. Generally, the bond wires 112 are kept as short aspossible in order to minimise radio frequency signal losses, as well asto reduce the area taken up by the integrated RF PA system 100, which isespecially useful when using CMOS devices.

Due to the closeness of many of the inductive components within theintegrated RF PA system 100, there are a number of potentiallyproblematic effects. For example, there can be mutual coupling betweenthe bond wires 112 and the power combiner elements 152, 172 of theintegrated power combiner devices 150, 170. There may also be mutualcoupling between the power combiner elements 152 and 172 themselveswithin the integrated power combiner devices 150, 170. These can becaused by an imbalanced impedance transformation and poor common-modeharmonic suppression within the integrated power combiner devices 150,170. This problem is usually solved by increasing the spacing betweenthe integrated power combiner devices 150, 170. However, this is notalways a viable option for devices when trying to reduce the overallsize of the integrated system 100.

Another common problem is centre-tap harmonic bounce at the connectors114 between the IC 102 and integrated power combiner devices 150, 170.This, again, can be caused by an imbalanced impedance transformation andpoor common-mode harmonic suppression.

Thus, a need exists for an improved coupling regime between RF IC 102and integrated power combiner devices 150, 170.

Referring now to FIG. 2, there is illustrated a simplified known powercombiner 200 that may be utilised in FIG. 1, for example, within theintegrated power devices 150, 170. Simplified known power combiner 200comprises two primary windings 201, 203, operably coupled to inputconnectors 205, and further operably coupled to each other via centretap connector 207, and secondary winding 209, which is somewhat isolatedfrom the two primary windings 201, 203.

A schematic diagram of the layout of such a simplified known powercombiner 200 is illustrated in 250, which comprises a series of primarywindings 260, 270, 280, 290 that are isolated from each other, and a‘figure 8’ layout for the secondary winding 254. Each isolated primarywinding 260, 270, 280, 290 comprises an interleaved structure 252situated above and below the secondary winding 254, which reduces lossesand enhances magnetic coupling. Due to the ‘figure 8’ layout for thesecondary winding 254, the secondary winding is somewhat immune tocommon mode disturbances because the incoming magnetic flux inducescurrents of opposite direction across each ‘figure 8’ section. In thiscase, the interleaved structure 252 of the primary windings 260, 270,280, 290 are operably coupled to each other at supply modules 256. Inthis case, the ‘figure 8’ secondary winding 254 is operably inductivelycoupled to all of the primary windings, 260, 270, 280, 290.

An illustration of current flows in schematic diagram 250 areillustrated in 295, which comprises a section of secondary winding 254,and primary winding 260. In this illustration, the interleaved structure252 of primary winding 260 has been offset to illustrate current flowsin each part of the interleaved structure 252. The interleaved structure252 of the primary winding 260 facilitates coupling above and below thesection of the secondary winding 254.

From the illustration of current flows in 295, it should be clear thatthe series of primary windings 260, 270, 280, 290 are not in ‘figure-8’structures, but a series of non-figure-8′ shaped primaries that areisolated from each other. Further, the resultant current flow insecondary winding 254 runs perpendicular to the current in the series ofprimary windings 260, 270, 280, 290.

A potential problem with this structure is that the primary windings260, 270, 280, 290 will still couple to each other, which would resultin an imbalanced impedance transformation and poor common-mode harmonicsuppression at each differential port. In some severe cases, animbalanced impedance transformation may affect the output power andefficiency of this structure.

It is known that mutual coupling can be a serious problem for certaindevices, for example radio frequency transceivers, as the effect ofmutual coupling can change antenna array radiation patterns and altermatching characteristics of antenna elements. Thus, a need exists for animproved power combiner for an IC.

In some cases, it may be desirable to suppress the common-mode power ofa power combiner. In the field of this invention, this is achieved byterminating at the fundamental frequency of a power amplifier.

Thus, a need exists for an improved power combiner, a transformer and atermination arrangement for a radio frequency transmitter, for example apower combining IC.

SUMMARY

Accordingly, the invention seeks to mitigate, alleviate or eliminate oneor more of the above mentioned disadvantages singly or in anycombination. Aspects of the invention provide a power combiner for aradio frequency power device, and a radio frequency transmittercomprising a power combiner as described in the appended claims.

According to a first aspect of the invention, there is provided a powercombiner for a radio frequency (RF) transmitter comprises a first planarfigure-8 shaped primary winding; and a first planar figure-8 shapedsecondary winding; wherein, the first planar figure-8 shaped primarywinding is substantially overlaid with the first planar figure-8 shapedsecondary winding. In this manner, such a figure-8 structure may providesymmetric coupling between primary winding(s) and secondary winding(s),thereby providing an opportunity to reduce mutual coupling between therespective windings.

Thus, in one example embodiment of the invention, the current flowingthrough a first section of the first planar figure-8 shaped primarywinding may be reversed when compared to current flowing through asecond section of the first planar figure-8 shaped primary winding,thereby forming anti-phase induced magnetic fields between the firstsection and second section of the first planar figure-8 shaped primarywinding. When the current flowing through a first section of the firstplanar figure-8 shaped secondary winding is also reversed when comparedto current flowing through a second section of the first planar figure-8shaped secondary winding, thereby forming additional anti-phase inducedmagnetic fields between the first section and second section of thefirst planar figure-8 shaped secondary winding, constructive andpower-efficient combination of signals at an output port may beachieved.

According to an optional feature of the invention, the power combinermay further comprise a second planar figure-8 shaped primary windingthereby forming a figure-88 shaped primary winding; and a second planarfigure-8 shaped secondary winding thereby forming a figure-88 shapedsecondary winding; wherein, the figure-88 shaped primary winding may besubstantially overlaid with the figure-88 shaped secondary winding. Inthis manner, the coupling between first primary winding and secondprimary winding may be configured to be reduced, or cancelledaltogether, due to a configured phase mismatch between generatedmagnetic fields.

According to an optional feature of the invention, a plurality of thefirst planar figure-8 shaped primary and secondary windings may beformed from two substantially oval-shaped tracks that may be operablycross coupled substantially at a mid-point of a longest length of theoval shape.

According to an optional feature of the invention, the overlaid locationof the figure-88 shaped primary winding and figure-88 shaped secondarywinding may be operable to facilitate reduction of inductive coupling.

According to an optional feature of the invention, the planar figure-8shaped primary windings may be coupled to the planar figure-8 shapedsecondary windings in a symmetrical manner.

According to an optional feature of the invention, the first planarfigure-8 shaped primary winding and second planar figure-8 shapedprimary windings may each comprise a first and second coupling portwherein, current may be operable to flow into the first coupling portand out of the second coupling port.

According to an optional feature of the invention, the current operableto flow into the first coupling port may have a magnetic field that isout of phase with a current operable to flow out of the second couplingport. In one example, a phase difference between the current operable toflow into the first coupling port and the current operable to flow outof the second coupling port may be substantially an odd multiple of awavelength (π) of a signal being carried by the power combiner. In oneexample, the phase difference between the current operable to flow intothe first coupling port and the current operable to flow out of thesecond coupling port may be operable to reduce coupling between thefirst planar figure-8 shaped primary winding and the second planarfigure-8 shaped primary winding

According to an optional feature of the invention, the first planarfigure-8 shaped secondary winding and second planar figure-8 shapedsecondary winding each comprise a first and second port arranged tosupport differential excitation.

According to an optional feature of the invention, the second port (‘2’)of the first planar figure-8 shaped secondary winding may be operablycoupled to the second port (‘4’) of the second planar figure-8 shapedsecondary winding, thereby supporting mirror differential excitationvoltage mode combining.

According to an optional feature of the invention, the first port (‘1’)of the first planar figure-8 shaped secondary winding may be arranged toprovide an output voltage following mirror differential excitationvoltage mode combining.

According to an optional feature of the invention, the second port (‘2’)of the first planar figure-8 shaped secondary winding may be operablycoupled to the first port (‘3’) of the second planar figure-8 shapedsecondary winding, thereby supporting sequential differential excitationvoltage mode combining.

According to an optional feature of the invention, the first port (‘1’)of the first planar figure-8 shaped secondary winding may be arranged toprovide an output voltage following sequential differential excitationvoltage mode combining.

According to an optional feature of the invention, the second port (‘2’)of the first planar figure-8 shaped secondary winding may be operablycoupled to the first port (‘3’) of the second planar figure-8 shapedsecondary winding and provide an output current, thereby supportingmirror differential excitation current mode combining.

According to an optional feature of the invention, the first port (‘1’)of the first planar figure-8 shaped secondary winding may be operablycoupled to the first port (‘3’) of the second planar figure-8 shapedsecondary winding and may provide an output current, thereby supportingsequential differential excitation current mode combining

According to a second aspect of the invention, there is provided a radiofrequency transmitter comprising a power combiner comprising: a planarfigure-8 shaped primary winding; and a planar figure-8 shaped secondarywinding; wherein, the planar figure-8 shaped primary winding issubstantially overlaid with the planar figure-8 shaped secondarywinding.

These and other aspects of the invention will be apparent from, andelucidated with reference to, the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details, aspects and embodiments of the invention will bedescribed, by way of example only, with reference to the drawings.Elements in the figures are illustrated for simplicity and clarity andhave not necessarily been drawn to scale. Like reference numerals havebeen included in the respective drawings to ease understanding.

FIG. 1 illustrates a known example of a RF PA integrated system.

FIG. 2 illustrates a known example of a RF power combiner.

FIG. 3 illustrates an example block diagram of a simplified wirelesscommunication unit, according to aspects of the invention.

FIG. 4 illustrates an example of a modified integrated RF PA systemincorporating aspects of the invention.

FIG. 5 illustrates an example of a power combiner utilising aspects ofthe invention.

FIG. 6 illustrates a further example of an alternative power combinerutilising aspects of the invention.

FIG. 7 illustrates a yet further example of an alternative powercombiner utilising aspects of the invention.

FIG. 8 illustrates an example implementation of a power combiner.

FIG. 9 illustrates an example of termination in a power combinerutilising aspects of the invention.

DETAILED DESCRIPTION

Examples of the invention will be described in terms of a power combinerfor a radio frequency (RF) transmitter that comprises a planar figure-8shaped primary winding; and a planar figure-8 shaped secondary winding;wherein, the figure-8 shaped primary winding is substantially overlaidwith the figure-8 shaped secondary winding. In this manner, such afigure-8 structure may provide symmetric coupling between the primarywinding(s) and secondary winding(s), thereby providing an opportunity toreduce mutual coupling between the respective windings. However, it willbe appreciated by a skilled artisan that the inventive concept hereindescribed may be embodied in any type of RF transmitter and/or powercombiner comprising: a primary winding and a secondary winding.

Examples of the invention will also be described in terms of a currentflowing through a first section of the planar figure-8 shaped primarywinding being reversed when compared to current flowing through a secondsection of the planar figure-8 shaped primary winding, thereby forminganti-phase induced magnetic fields between the first section and secondsection of the first primary winding. Similarly, when the currentflowing through a first section of the planar figure-8 shaped secondarywinding is also reversed when compared to current flowing through asecond section of the planar figure-8 shaped secondary winding,additional anti-phase induced magnetic fields between the first sectionand second section of the secondary winding may be formed, andconstructive and power-efficient combination of signals at an outputport may be achieved. As such, hereinafter for some example embodiments,the terms primary winding and secondary winding may be interchanged, aswould be appreciated by a skilled artisan.

Some examples of the invention are also described with regard to thepower combiner further comprising a second planar figure-8 shapedprimary winding, which together with the first planar figure-8 shapedprimary winding thereby forms a figure-88 shaped primary winding; and asecond planar figure-8 shaped secondary winding, which together with thefirst planar figure-8 shaped secondary winding thereby forms a figure-88shaped secondary winding; wherein, the figure-88 shaped primary windingmay be substantially overlaid with the figure-88 shaped secondarywinding. In this manner, the coupling between first primary winding andsecond primary winding may be configured to be reduced, or cancelledaltogether, due to a configured phase mismatch between generatedmagnetic fields

Although examples of the invention will be described in terms ofsubstantially oval-shaped tracks that are operably cross coupledsubstantially at a mid-point of a longest length of the oval shape, itis envisaged that other shaped track designs and/or cross coupling atother than an accurate mid-point of a longest length of the oval shapemay be used. Furthermore, although examples of the invention will bedescribed in terms of substantially overlaying a figure-8 or figure-88shaped primary winding with a figure-8 or figure-88 shaped secondarywinding, it is envisaged that the overlaying may be configured to besufficient to induce the corresponding desired induced magnetic fields,and therefore, in some examples, the respective winding structures maynot need to be wholly accurately overlain with one another.

Some examples of the invention are also described with regard tosupporting mirror differential excitation current mode combining and/orsequential differential excitation voltage mode combining. However, itis envisaged that the inventive concept may be applied to other forms ofpower combining.

Referring first to FIG. 3, a block diagram of a wireless communicationunit (sometimes referred to as a mobile subscriber unit (MS) in thecontext of cellular communications or a user equipment (UE) in terms ofa 3^(rd) generation partnership project (3GPP™) communication system) isshown, in accordance with one example embodiment of the invention.

The wireless communication unit 300 contains a transceiver having anantenna 302 coupled to an antenna switch or a duplexer 304. Further, thereceiver chain, as known in the art, includes receiver front-endcircuitry 306 (effectively providing reception, filtering andintermediate or base-band frequency conversion). The front-end circuitry306 is serially coupled to a signal processing function 308. An outputfrom the signal processing function 308 is provided to a suitable outputdevice 310, such as a screen or flat panel display. The receiver chainalso includes a controller 314 that maintains overall subscriber unitcontrol. The controller 314 is also coupled to the receiver front-endcircuitry 306 and the signal processing function 308 (generally realisedby a digital signal processor (DSP)). The controller is also coupled toa memory device 316 that selectively stores operating regimes, such asdecoding/encoding functions, synchronisation patterns, code sequences,and the like. A timer 318 is operably coupled to the controller 314 tocontrol the timing of operations (transmission or reception oftime-dependent signals) within the wireless communication unit 300.

As regards the transmit chain, this essentially includes an input device320, such as a keypad, coupled in series via signal processor function308 through transmitter/modulation circuitry 322 and a power amplifier324 to antenna 302. A coupler 312 is typically located between the poweramplifier 324 and the antenna 302 and arranged to route a portion of thetransmit signal (that is output to the antenna 302) to basebandprocessing circuitry via feedback path 313, for example located ineither transmitter/modulation circuitry 322 or signal processor function308. The transmitter/modulation circuitry 322 and the power amplifier324 are operationally responsive to the controller 314.

In this example, wireless communication unit 300 may optionally employan integrated power device 330 between the output of the power amplifier324 and the input to antenna switch or duplexer 304. Various conceptsfor integrated power device 330 are illustrated in one or more laterfigures. In some examples, the integrated power device 330 may receivemore than one coupled signal from the output of power amplifier 324. Insome examples, the more than one coupled signal may be a differentialpair of signals, which may, in some examples, be cross coupled withother differential pairs of signals from other power amplifiers (notshown). Thus, in some examples, power amplifier 324 may comprise aplurality of power amplifiers.

Referring now to FIG. 4, a block diagram of an example integrated powercombiner device 440 is shown with respective coupled components,according to some examples of the invention. FIG. 4 comprises, poweramplifier modules 324, 325 operably cross-coupled, via a first pair ofbond wires 404, 405 and a second pair of bond wires 406, 407, to nodesof integrated power combiner device 440, which may in some examples be apower combiner module. The bond wires 404, 405, 406, 407 may be formedof any suitable metal or alloy, for example copper or aluminium. In thisexample, the first pair of bond wires 404, 405 and the second pair ofbond wires 406, 407 may each form a differential pair of bond wires. Inthis example, the bond wires 404, 405, 406, 407 may range from, forexample, 100 μm to 2 mm. Further, the coupling distance between the bondwires 404, 405, 406, 407 may be user defined, with a minimum couplingdistance of around 50 μm.

Therefore, current flowing within the first pair of bond wires 404, 405may have opposing phase between bond wire 404 and bond wire 405.Similarly, current flowing within the second pair of bond wires 406, 407may have opposing phase between bond wire 406 and bond wire 407. As aresult, any inductively induced magnetic fields within the first pair ofbond wires 404, 405 may exhibit an opposing magnetic field in bond wire404 when compared to bond wire 405. Similarly, any inductively inducedmagnetic fields within the second pair of bond wires 406, 407 mayexhibit an opposing magnetic field in bond wire 406 when compared tobond wire 407. In this example, the first pair of bond wires 404, 405may be cross coupled with respect to the second pair of bond wires 406,407 to nodes within integrated power device 440, thereby forming a setof double cross-coupled bond wires. Further, the opposing magneticfields within the first pair of bond wires 404, 405 and the second pairof bond wires 406, 407 may exhibit the effect of reducing magneticcoupling between the respective bond wires. Furthermore, magneticcoupling may be reduced between the bond wires 404, 405, 406, 407 andinductive elements of the integrated power device 440 due to theopposing magnetic fields within the first pair of bond wired 404, 405and the second pair of bond wires 406, 407. Inductive elements of theintegrated power device may comprise, for example, first primary winding420 and/or second primary winding 470.

An example of current flow between power amplifier modules 324, 325 andintegrated power combiner device 440 is shown by arrows in FIG. 4. Itshould be noted that this is only one possible configuration for currentflow, and it is possible that the current flows denoted by the arrowscan be reversed or altered to provide a similar result without deviatingfrom concepts of the invention.

In some examples, bond wires 404 and 406 may be considered as a firstpair of cross-coupled bond wires and bond wires 405 and 407 may beconsidered as a second pair of cross-coupled bond wires. In thisexample, bond wire 404 of the first pair of bond wires may be operablycoupled to node (1) of the power amplifier module 324 and node (3′) ofthe integrated power combiner device 440. Further, bond wire 406 of thesecond pair of bond wires may be operably coupled to node (3) of thepower amplifier module 324 and node (1′) of the integrated powercombiner device 440.

Further, the current from cross coupled bond wires 404 and 406 may bereceived at nodes (3′) and (1′) respectively, and combined at node 5422, which may be situated between node (1′) and first primary winding420 of integrated power combiner device 440. The current flowing in bondwires 404 and 406 may be in-phase, and may be cross-coupled before beingreceived at integrated power combiner device 440. In some examples, node(5′) 422 may form a first differential node for first primary winding420.

In this case, there may be a fixed current at node (5′) that may beformed from a combination of received currents from cross-coupled bondwires 404 and 406, which may be in-phase with respect to each other.Therefore, current at node (5′) may flow through first primary winding420 to node (6′) 424. In some examples, node (6′) 424 may form a seconddifferential node for first primary winding 420, whereby the current maybe distributed from node (6′) 424 to nodes (2′) and (4′). In this case,bond wire 405 of the first pair of bond wires may be operably coupled tonode (4′) of the integrated power combiner device 440 and node (2) ofthe power amplifier modules 324. Further, bond wire 407 of the secondpair of bond wires may be operably coupled to node (2′) of theintegrated power combiner device 440 and node (4) of the power amplifiermodules 324.

In some further examples, the current flow between bond wires 404, 407and 406, 405 may form a pseudo figure-8 shaped current loop, which mayfurther reduce magnetic coupling between bond wires 404, 405, 406, 407,and inductive components of the integrated power combiner device 440.For example, current at node (1) may flow, via bond wire 404, throughfirst primary winding 420 via nodes (3′) and (5′), and return to node(2), via bond wire 405, via nodes (6′) and (4′). Further, current mayflow at node (3), via bond wire 406, through first primary winding 420via nodes (1′) and (5′), and return to node (4), via bond wire 407, vianodes (6′) and (2′).

Therefore, in this example, the current flow between bond wires 404, 407and 406, 405 forms pseudo figure-8 shaped current paths, which mayreduce magnetic coupling between the bond wires, particularly in on-chipinductive components. In this manner, double cross-coupled bond wiresbetween the PA integrated circuit and the integrated power combinerdevice 440 may be able to reduce any mutual coupling effect between theinductive components of the integrated power combiner device 440 and thebond wires.

In some examples, the above operation of the double cross-coupled bondwires operably coupling an output of power amplifiers 324, 325 with anintegrated power combiner device 440 may be repeated for secondaryregion 450, which may comprise a further set of double cross-coupledbond wires 460, power amplifier module 324 and a second primary winding470. In some examples, power amplifier module 324 may comprise aplurality of power amplifier modules.

One advantage of utilising double cross-coupled bond wires may be thatmutual coupling between the cross-coupled bond wires and inductivecomponents within the integrated power combiner device 440 may bereduced. In some examples, the opposing phase and current flow betweenbond wires 404 and 405 of the first pair of bond wires may induceopposite magnetic fields in the two bond wires 404 and 405. This maycause electromagnetic field cancellation within the first pair of bondwires 404, 405. Similarly, the opposing phase and current flow betweenbond wires 406 and 407 of the second pair of bond wires may induceopposite magnetic fields in the two bond wires 406 and 407. This mayalso cause electromagnetic field cancellation within the second pair ofbond wires 406, 407.

In this manner, by utilising electromagnetic field cancellation betweenbond wires, an improvement in power efficiency in transferring radiofrequency power from the inputs of a plurality of power amplifierdevices 324, 325 to an output of an integrated power combiner device 440may be achieved. Furthermore, such an improvement may be achievedwithout increasing the spacing between the bond wires and the inductivecomponents in integrated power combiner devices.

In some examples, the current flowing in bond wires and integrated powercombiner device 440 may approximate a double 8-shaped current loop.

Although the examples illustrated in FIG. 4 are shown with centre-tappedprimary windings, it should be noted that, in other examples, a singularinductive element winding, may be utilised with the invention or aplurality of inductive elements that may or may not be centre-tapped.

In some examples, cross-coupled bond wires 404 and 406 may form a firstpair of cross-coupled bond wires that may be operably coupled to asecond input terminal, which may be a positive terminal, of firstprimary winding 420.

In this example, the first pair of cross-coupled bond wires 404, 406 maybe output from different power amplifier modules 324, 325 to arespective one of a plurality of paired output terminals (1-2; 3-4),where a pair of output terminals are coupled between a respectiveamplifier stage and a first paired input terminal (1′-3′ or 2′-4′). Thefirst paired input terminal (1′-3′ or 2′-4′) is then connected to arespective second input terminal (5′, 6′). Further, cross coupled bondwires 405 and 407 may form a second pair of cross coupled bond wires.These nodes (2′) and (4′) may be operably coupled to a second terminal,which may be a negative terminal, of first primary winding 420, whichmay be node (6′) (424).

In this example, a second pair of cross-coupled bond wires 405 and 407may be operably coupled to nodes (2) and (4) of the different poweramplifier modules. In this example, a first power amplifier module 324may comprise nodes (1) and (2), and a second power amplifier module 325may comprise nodes (3) and (4). Further, the positive terminal node (5′)(422) of first primary winding 420 may comprise nodes (1′) and (3′), andthe negative terminal (6′) (424) of first primary winding 420 maycomprise nodes (2′) and (4′). In this example, current may flow fromoutput terminals (1) and (3) to second input terminal (5′) 422, viafirst paired input terminals (3′) and (1′). Thereafter, the current mayflow out of second input terminal (6′) 424 to output terminals (2) and(4), via paired output terminals (2′) and (4′), thereby forming aplurality of figure-8 loops.

Referring now to FIG. 5, an example of an alternative power combiner 500is illustrated that utilises aspects of the invention. A power combinerschematic 540 is used to illustrate how parts of alternative powercombiner 500 may be utilised in combination. In this example, powercombiner schematic 540 may comprise two primary windings 542, 544, whichmay be operably coupled to each other via a centre tap 546, as well asbeing magnetically coupled to secondary windings 548, 549.

Referring now to alternative power combiner 500, there is illustrated analternative primary winding layout 512, 524 according to aspects of theinvention. In this example, first primary winding 512 may comprise afigure-8 type layout, wherein current I1 may flow through the figure-8type layout according to arrows 514 and 515. In this example, thecurrent flowing through first section 516 (denoted by current flow 514)of first primary winding 512 is reversed when compared to the currentflowing through second section 518 (denoted by current flow 515) offirst primary winding 512. Therefore, any magnetic fields induced in thefirst section 516 of first primary winding 512 may be anti-phasecompared to any induced magnetic fields in the second section 518 offirst primary winding 512. Similarly, referring now to second primarywinding 524 that may also comprise a figure-8 type layout, whereincurrent I1 flows through the figure 8 type layout according to arrows526 and 527. In this example, the current flowing through the firstsection 528 (denoted by current flow 527) of second primary winding 524is reversed when compared to the current flowing through second section530 (denoted by current flow 526) of second primary winding 524. As aresult, any induced magnetic fields in the first section 528 and secondsection 530 of second primary winding 524 may be anti-phase whencompared to each other.

In this manner, the power combiner of FIG. 5, which is suitable for aradio frequency (RF) transmitter, comprises a first 512 planar figure-8shaped primary winding located adjacent a second 524 planar figure-8shaped primary winding, which in combination thereby form a figure-88shaped primary winding. Additionally, a first 550 planar figure-8 shapedsecondary winding located adjacent a second 570 planar figure-8 shapedsecondary winding forms a figure-88 shaped secondary winding. Notably,when the figure-88 shaped primary winding is substantially overlaid withthe figure-88 shaped secondary winding, the coupling between firstprimary winding 512 and second primary winding 524 may be reduced, orcancelled altogether, due to a configured phase mismatch betweengenerated magnetic fields.

In this example, primary windings 512, 524 may be coupled with secondarywindings 550, 570, which may also comprise a figure-8 type structure. Inthis case, primary windings 512, 524 may be positioned substantiallyover or under secondary windings 550, 570 in such a way as to maximisecoupling between primary windings 512, 524 and secondary windings 550,570. Therefore, current flowing through secondary windings 550, 570 maybe substantially the reverse of that in corresponding primary windings512, 524. Utilising the figure-8 structure for primary 512, 524 andsecondary windings 550, 570 may allow for symmetric coupling betweenprimary windings 512, 514 and secondary windings 550, 570, therebypotentially reducing any mutual coupling between windings. Further, eachfigure-8 shaped primary 512, 524 may be operably coupled to eachcorresponding figure-8 shaped secondary 550, 570. Utilising the figure-8structure may further reduce coupling between primary windings 512 and524.

In one example, a plurality of the first planar figure-8 shaped primaryand secondary windings (512,524, 550, 570) may be formed from twosubstantially oval-shaped tracks that are operably cross coupledsubstantially at a mid-point of a longest length of the oval shape.

Referring now to FIG. 6, examples of the ‘figure-88 power combiner’ ofFIG. 5 are illustrated, whereby the planar figure-8 shaped primarywindings are coupled to the planar figure-8 shaped secondary windings550, 570 in a symmetrical manner. Additionally, in FIG. 6, examples of afigure-88 power combiner employing mirror differential excitation 605and sequential differential excitation 650 forms of voltage-mode powercombining are illustrated. Thus, in order to support differentialexcitation the first and second planar figure-8 shaped primary windingseach comprise a first and second input port arranged to supportdifferential excitation. Furthermore, the first and second planarfigure-8 shaped secondary windings each comprise a first and secondoutput/coupling port arranged to support differential excitation.

In these examples, mirror differential excitation 605 refers to, andencompasses, the input signal's phase relationship between windings 608,610 and windings 612, 614. For example, in mirror differentialexcitation 605, the current flowing in windings 608, 610 is ‘mirrored’in windings 612, 614. Therefore, the current flow is ‘mirrored’ inwindings 612, 614, compared to windings 608, 610, leading to a phasechange in current flowing between the two sets of windings.

In sequential differential excitation 650, current flows sequentially inwindings 655, 660 and windings 665, 670. Therefore, there is no‘mirroring’ in this example, which negates any phase change in currentflowing between the two sets of windings.

In some examples, mirrored differential excitation 605 and sequentialdifferential excitation 650 alter the phase of each transformer, whichmay alter output port combinations.

Referring first to mirror differential excitation 605, power amplifiermodules 607 may be operably coupled, via bond wires 609, to primarywindings 608 of power combiner 605 that are denoted by solid lines. Insome examples, bond wires 609 may be double cross-coupled bond wires.

In this example, outputs from secondary windings 610, 614, denoted byhashed lines, may be coupled in a variety of ways. In this example,negative output port (2) of secondary winding 610 and positive outputport (4) of secondary winding 614 may be operably coupled together,leading to a 2*V2 voltage at output port (1) of secondary windings 610.Further, output port (3) may be operably coupled to ground. In thisexample, port (1) may have positive polarity and port (2) may havenegative polarity. These polarities may be mirrored in ports (3) and(4), wherein port (3) may have negative polarity and port (4) may havepositive polarity.

Thus, in this manner, the second port (2) of the first planar figure-8shaped secondary winding 610 is operably coupled to the second port (4)of the second planar figure-8 shaped secondary winding 614, therebysupporting mirror differential excitation voltage mode combining. Inthis example, the first port (1) of the first planar figure-8 shapedsecondary winding 610 is arranged to provide an output current followingmirror differential excitation voltage mode combining.

Referring now to 650, power amplifier modules 651 may be operablycoupled, via bond wires 652, to primary windings 655 of power combiner650 that are denoted by solid lines. In some examples, bond wires 652may be double cross coupled bond wires. In this example, outputs fromsecondary windings 660, denoted by hashed lines, may be coupled in avariety of ways. In this example, negative output port (2) may have beenoperably coupled to positive output port (3), leading to a 2*V2 voltageat port (1) of secondary windings 660. Further, output port (4) may havebeen operably coupled to ground. In this example, ports (1) and (3) ofsecondary windings 660 may have positive polarities and ports (2) and(4) of secondary windings 660 may have negative polarities.

Thus, in this manner, the second port (2) of the first planar figure-8shaped secondary winding 660 is operably coupled to the first port (3)of the second planar figure-8 shaped secondary winding 670, therebysupporting sequential differential excitation voltage mode combining. Inthis example, the first port (1) of the first planar figure-8 shapedsecondary winding 660 is arranged to provide an output current followingsequential differential excitation voltage mode combining.

In some examples, power combiners 605 and 650 may be utilised withseries connections to a plurality of other power combiners in order tosum output voltages at each power combiner. In some examples, this maybe achieved by ‘stacking’ the plurality of power combiners 605, 650together in series. In some cases, each of the plurality of powercombiners 605, 650 may have different excitations that have differentphase values at the output of the power combiner coils. By configuringthe output connections from the secondary windings 610, 660, the‘Stacked output’ may exhibit in-phase combined voltage at the output.

It should be noted that other layouts and polarities of the nodes areenvisaged within the concepts herein described, and the illustratedexamples relating to FIG. 6 should not be seen as limiting.

Referring now to FIG. 7, yet further examples of the ‘figure-88 powercombiner’ of FIG. 5 are illustrated utilising mirror differentialexcitation 705 and sequential differential excitation 750 forms ofcurrent-mode power combining. Referring first to mirror differentialexcitation 705, power amplifier modules 707 may be operably coupled, viabond wires 709, to primary windings 708 of power combiner 705 that aredenoted by solid lines. In some examples, bond wires 709 may be doublecross coupled bond wires. In this example, outputs from secondarywindings 710, 714 denoted by hashed lines, may be coupled in a varietyof ways. For example, negative output port (2) and negative output port(3) of secondary windings 710 may be operably coupled together, leadingto a 2*I2 output current at these nodes. Further, output ports (1) and(4) of secondary windings 710, 714 may be operably coupled to ground. Inthis example, output ports (1) and (4) of secondary windings 710, 714may have positive polarity and output port (2) of secondary winding 710and port (3) of secondary winding 714 may have negative polarity.

Thus, in this manner, the second port (2) of the first planar figure-8shaped secondary winding 710 is operably coupled to the first port (3)of the second planar figure-8 shaped secondary winding 714 and providean output current 716, thereby supporting mirror differential excitationcurrent mode combining.

Referring now to 750, power amplifier modules 751 may be operablycoupled, via bond wires 752, to primary windings 755, 765 of powercombiner 750 that are denoted by solid lines. In some examples, bondwires 752 may be double cross coupled bond wires. In this example,outputs from secondary windings 760, 770 denoted by hashed lines, may becoupled in a variety of ways. In this example, positive output port (1)of secondary winding 760 and port (3) of secondary winding 770 may beoperably coupled together, leading to a 2*I2 output current 775 at thesenodes. Further, output port (2) of secondary winding 760 and port (4) ofsecondary windings 770 may be operably coupled to ground. In thisexample, output port (1) of secondary winding 760 and port (3) ofsecondary windings 770 may have positive polarity and output port (2) ofsecondary winding 760 and port (4) of secondary windings 770 may havenegative polarity.

Thus, in this manner, the first port (1) of the first planar figure-8shaped secondary winding 760 is operably coupled to the first port (3)of the second 770 planar figure-8 shaped secondary winding and providean output current 775, thereby supporting sequential differentialexcitation current mode combining.

In some examples, power combiners 705 and 750 may be utilised withparallel connections to a plurality of other power combiners in order tosum output currents at each power combiner. In some examples, this maybe achieved by ‘stacking’ the plurality of power combiners 705, 750together in parallel. In some cases, each of the plurality of powercombiners 705, 750 may have different excitations that have differentphase values at the output of the power combiner coils. By configuringthe output connections from the secondary windings 710 or 760 and 770,the ‘Stacked output’ may have in-phase combined current at the output.

The illustrated examples in FIG. 6 and FIG. 7 may have substantially thesame example advantages as recited for the illustrated examples given inFIG. 5. For example, an effect of the figure-8 structures may be thatcoupling between primary windings and secondary windings may be reduced,or in some examples cancelled altogether, due to a phase mismatchbetween magnetic fields. Further, the figure 8 structures of the primarywindings and secondary windings may enhance coupling between thewindings. Further, the figure-8 structure may potentially reduce anymutual coupling between first and second sections of primary andsecondary windings. In other examples, any number of primary windingsand/or secondary windings may be utilised in conjunction with any numberof power amplifier modules.

Further, in some examples, utilising mirror and sequential differentialexcitation in FIG. 6 and FIG. 7 may reduce and/or cancel couplingbetween adjacent transformers, without reducing or cancelling couplingbetween primary and secondary windings of the transformers.

In some examples, the bond wires 609 of the mirror differentialexcitation power combiner and sequential differential excitation form ofvoltage-mode power combining may comprise cross-coupled bond wires otherthan double cross-coupled bond wires, as illustrated in FIG. 8.

Referring now to FIG. 8, an example implementation utilisingconventional T-core power combiners 805, 850 is illustrated.

In this example, Tcore power combiner 805 may utilise a mirrordifferential excitation form of voltage-mode power combining, whereasTcore power combiner 850 may utilise a sequential differentialexcitation form of voltage-mode power combining. Referring first to themirror differential excitation Tcore power combiner 805, power amplifiermodules 807 may be operably coupled, via bond wires 809, to primarywindings 808, 811 of mirror differential excitation Tcore power combiner805 that are denoted by solid lines. In this example, due to theasymmetric nature of the mirror differential excitation Tcore powercombiner 805, the polarities at the primary windings 808, 811 may bereversed when compared to corresponding polarities at the secondarywindings 810, 812, denoted by hashed lines. In this example, positiveoutput port (2) may be operably coupled to negative output port (4) ofsecondary windings 810, 812, leading to a 2*V2 voltage at output port(1) of secondary windings 810, 812. Further, output port (2) may beoperably coupled to ground. In this example, port (1) and port (4) mayhave negative polarity, and port (2) and port (3) may have positivepolarity.

Referring now to 850, power amplifier modules 851 may be operablycoupled, via bond wires 852, to primary windings 855, 856 of sequentialdifferential excitation Tcore power combiner 850 that are denoted bysolid lines. In this example, due to the asymmetric nature of thesequential differential excitation Tcore power combiner 850, polaritiesat the primary windings 855, 856 may be reversed when compared tocorresponding polarities at secondary windings 860, 861, denoted byhashed lines. In this example, positive output port (2) may be operablycoupled to negative output port (3), of secondary windings 860, 861,leading to a 2*V2 voltage at output port (1) of secondary windings 860.Further, output port (4) may be operably coupled to ground. In thisexample, output ports (1) and (3) may have negative polarity, and outputports (2) and (4) may have positive polarity.

Referring to FIG. 9, an example of a termination module for a powercombiner module 900 is illustrated. In this example, power combinermodule 900 may comprise at least one centre tapped primary winding 902,coupled to at least one output secondary winding 904.

Generally, in the art, the centre tapped primary windings 902 aregrounded, or impedance matched to the fundamental frequency of a circuitthat they are utilised with. However, circuits of this type still sufferfrom parasitic impedances and imbalanced impedance transformations. Theinventors have recognised and appreciated that these problems may, inpart, be due to poor harmonic suppression.

Therefore, in accordance with some examples, power combiner module 900,employs at least one harmonic termination module 906. In a powercombiner with two primary windings, one example of the invention maycouple at least one harmonic termination module 906 to each centretapped primary winding 902, as shown. In this example, the at least onetermination module 906 may comprise at least one harmonic terminationcircuit, for example a notch filter frequency response, configured for agiven harmonic frequency of a device utilising the power combiner module900. In some other examples, the at least one termination module 906 maycomprise a plurality of terminations for a plurality of harmonicfrequencies.

In this example, harmonic terminations in a form of a notch filter maycomprise at least one charge storage device (e.g. a capacitor) in serieswith at least one inductive element, per frequency.

In one example, the at least one harmonic termination module 906 maycomprise terminations for fundamental frequency f0 908, and thirdharmonic frequency 3fc 912 of the power combiner 900. In this example,fundamental frequency f0 908 and third harmonic frequency terminations3fc 912 may be employed to reduce any common mode voltages that mayappear in the power combiner 900, for example by reducing any voltageswing on the centre taps 902 of power combiner 900.

In another example, second harmonic frequency termination 910 (and oneor more other even multiple harmonic terminations) may be utilised tominimise the effect of any second (or higher) harmonic leakage coupledback to primary windings 902 and 904.

Thus, one advantage of utilising the at least one termination module 906may be that power combiner 900 is more balanced due to lower PA outputimpedance values at harmonic frequencies present within power combiner900.

In a further example, a further power combiner 950 comprising a singleprimary winding 953, and a single secondary winding 954 operably coupledto a load 956, may have at least one harmonic termination module 906coupled to the primary winding 953. In this example, the at least oneharmonic termination module 906 may comprise at least one harmonictermination circuit, for example a notch filter frequency response,configured for a given harmonic frequency of a device utilising thepower combiner module 950. In some other examples, the at least onetermination module 906 may comprise a plurality of terminations for aplurality of harmonic frequencies. In this example, inductances 957 and958 relate to possible loading on the output 956, and do not relate toharmonic termination module 906.

In some other examples (not shown), it is envisaged that current may befed through one or more secondary windings of power combiner 900.Therefore, in this example, harmonic termination module 906 may beoperably coupled to one or more secondary windings of power combiner900.

Examples of the invention herein before described and illustrated in theFIGs may be used in isolation or in any combination. In particular, itis envisaged that the aforementioned inventive concept can be applied bya semiconductor manufacturer to any integrated circuit comprising radiofrequency circuits. In particular, the inventive concept can be appliedto any circuit comprising high power radio frequency combiners. It isfurther envisaged that, for example, a semiconductor manufacturer mayemploy the inventive concept in a design of a stand-alone device, suchas a RF power amplifier, duplexer, antenna switch, power combiner, orcorresponding application-specific integrated circuit (ASIC) and/or anyother sub-system element.

It will be appreciated that, for clarity purposes, the above descriptionhas described embodiments of the invention with reference to differentfunctional units. However, it will be apparent that any suitabledistribution of functionality between different functional units, forexample with respect to the coupling between the power amplifier stagesand antenna, may be used without detracting from the inventive conceptsherein described. Hence, references to specific functional units areonly to be seen as references to suitable means for providing thedescribed functionality, rather than indicative of a strict logical orphysical structure or organization.

Although the present invention has been described in connection withsome embodiments, it is not intended to be limited to the specific formset forth herein. Rather, the scope of the present invention is limitedonly by the accompanying claims. Additionally, although a feature mayappear to be described in connection with particular embodiments, oneskilled in the art would recognize that various features of thedescribed embodiments may be combined in accordance with the invention.In the claims, the term ‘comprising’ does not exclude the presence ofother elements or steps.

Additionally, although individual features may be included in differentclaims, these may possibly be advantageously combined, and the inclusionin different claims does not imply that a combination of features is notfeasible and/or advantageous. Also, the inclusion of a feature in onecategory of claims does not imply a limitation to this category, butrather indicates that the feature is equally applicable to other claimcategories, as appropriate.

Furthermore, the order of features in the claims does not imply anyspecific order in which the features must be performed and in particularthe order of individual steps in a method claim does not imply that thesteps must be performed in this order. Rather, the steps may beperformed in any suitable order. In addition, singular references do notexclude a plurality. Thus, references to ‘a’, ‘an’, ‘first’, ‘second’,etc. do not preclude a plurality.

Thus, an improved radio frequency transmitter, power combiners andtermination modules therefor have been described, wherein theaforementioned disadvantages with prior art arrangements have beensubstantially alleviated.

What is claimed is:
 1. A power combiner for a radio frequency, RF,transmitter comprising: a first planar figure-8 shaped primary windingconfigured to support current flow in a figure-8 pattern; a secondplanar figure-8 shaped primary winding that with the first planarfigure-8 shaped primary winding forms a figure-88 shaped primarywinding, the second planar figure-8 shaped primary winding beingconfigured to support current flow in a figure-8 pattern; a first planarfigure-8 shaped secondary winding configured to support current flow ina figure-8 pattern; and a second planar figure-8 shaped secondarywinding that with the first planar figure-8 shaped secondary windingforms a figure-88 shaped secondary winding, the second planar figure-8shaped secondary winding being configured to support current flow in afigure-8 pattern; wherein, the figure 8 figure-88 shaped primary windingis substantially overlaid with the figure 8 figure-88 shaped secondarywinding.
 2. The power combiner of claim 1, wherein the overlaid locationof the figure-88 shaped primary winding and figure-88 shaped secondarywinding is operable to facilitate reduction of inductive coupling. 3.The power combiner of claim 1, wherein a plurality of the first planarfigure-8 shaped primary and secondary windings are formed from twosubstantially oval-shaped tracks that are operably cross coupledsubstantially at a mid-point of a longest length of the oval shape. 4.The power combiner of claim 1, wherein current flowing through a firstsection of the of the first planar figure-8 shaped primary winding isreversed when compared to current flowing through a second section ofthe first planar figure-8 shaped primary winding, thereby forminganti-phase induced magnetic fields between the first section and secondsection of the first primary winding.
 5. The power combiner of claim 1,wherein the first planar figure-8 shaped primary winding and secondplanar figure-8 shaped primary windings each comprise a first and secondcoupling port wherein current is operable to flow into the firstcoupling port and out of the second coupling port.
 6. The power combinerof claim 5, wherein the current operable to flow into the first couplingport has a magnetic field that is anti-phase with a current operable toflow out of the second coupling port.
 7. The power combiner of claim 6,wherein a phase difference between the current operable to flow into thefirst coupling port and the current operable to flow out of the secondcoupling port is substantially an odd multiple of a wavelength of asignal being carried by the power combiner.
 8. The power combiner ofclaim 7, wherein the phase difference between the current operable toflow into the first coupling port and the current operable to flow outof the second coupling port is operable to reduce coupling between thefirst planar figure-8 shaped primary winding and the second planarfigure-8 shaped primary winding.
 9. The power combiner of claim 1,wherein the first planar figure-8 shaped secondary winding and secondplanar figure-8 shaped secondary winding each comprise a first andsecond coupling port arranged to support differential excitation. 10.The power combiner of claim 9, wherein a second port of the first planarfigure-8 shaped secondary winding is operably coupled to the second portof the second planar figure-8 shaped secondary winding, therebysupporting mirror differential excitation voltage mode combining. 11.The power combiner of claim 10, wherein a first port of the first planarfigure-8 shaped secondary winding is arranged to provide an outputvoltage following mirror differential excitation voltage mode combining.12. The power combiner of claim 9, wherein a second port of the firstplanar figure-8 shaped secondary winding is operably coupled to thefirst port of the second planar figure-8 shaped secondary winding,thereby supporting sequential differential excitation voltage modecombining.
 13. The power combiner of claim 12, wherein a first port ofthe first planar figure-8 shaped secondary winding is arranged toprovide an output voltage following sequential differential excitationvoltage mode combining.
 14. The power combiner of claim 9, wherein asecond port of the first planar figure-8 shaped secondary winding isoperably coupled to the first port of the second planar figure-8 shapedsecondary winding and provide an output current, thereby supportingmirror differential excitation current mode combining.
 15. The powercombiner of claim 9, wherein a first port of the first planar figure-8shaped secondary winding is operably coupled to the first port of thesecond planar figure-8 shaped secondary winding and provide an outputcurrent, thereby supporting sequential differential excitation currentmode combining.
 16. A radio frequency transmitter comprising a powercombiner comprising: a first planar figure-8 shaped primary windingconfigured to support current flow in a figure-8 pattern; a secondplanar figure-8 shaped primary winding that with the first planarfigure-8 shaped primary winding forms a figure-88 shaped primarywinding, the second planar figure-8 shaped primary winding beingconfigured to support current flow in a figure-8 pattern; a first planarfigure-8 shaped secondary winding configured to support current flow ina figure-8 pattern; and a second planar figure-8 shaped secondarywinding that with the first planar figure-8 shaped secondary windingforms a figure-88 shaped secondary winding, the second planar figure-8shaped secondary winding being configured to support current flow in afigure-8 pattern; wherein, the figure-88 shaped primary winding issubstantially overlaid with the figure-88 shaped secondary winding. 17.The radio frequency transmitter of claim 16, wherein a plurality of thefirst planar figure-8 shaped primary and secondary windings are formedfrom two substantially oval-shaped tracks that are operably crosscoupled substantially at a mid-point of a longest length of the ovalshape.
 18. The radio frequency transmitter of claim 16, wherein theoverlaid location of the figure-88 shaped primary winding and figure-88shaped secondary winding is operable to facilitate reduction ofinductive coupling.